The invention relates to a tool for machines for working stone and agglomerates of inert materials, particularly for polishing, facing, cutting, milling, sizing, shaping, rabbeting, squaring or beveling natural stone, such as porphyries, granites, marbles or synthetic stone such as for example ceramics, which comprises a support for the abrasive or, respectively, cutting material that is in contact with the stone during working and a connecting part for connecting the tool to the machine that generates and transmits to the tool the movement that said tool performs during working, the support and the connecting part being mutually fastened to each other in a fixed but detachable manner by way of removable locking means.
Such machines are known as using a plurality of tools which differ in terms of shape, dimensions and technical characteristics according to the type of work the tool is designed for.
During stone working, the machines cause the tools to perform repeated movements which are typical and specific for the type of work to be performed, such as back-and-forth straight-line motions, intermittent or stepwise straight-line movements, oscillations, continuous rotations in one direction, alternating rotations in two directions, etcetera, or even a movement which is a combination of two or more movements.
Said movement is generated by the machine and transmitted to the tool. For this purpose, the tool is connected to the machine through a connecting part, which is provided with appropriate connecting means, such as for example an insertion seat for an arm or for a chuck of the machine. The tool further has a support for the abrasive or, respectively, cutting material with which the stone is worked. Said support accommodates the abrasive or, respectively, cutting material with which the stone is worked. The material is diamond-impregnated, i.e., it contains a certain amount of diamond, which being harder than the stone, allows to work said stone.
In conventional tools, the support and the connecting part are currently fastened to each other in a fixed but detachable manner by way of removable locking means, such as for example screws, grub screws and the like. This allows to disassemble the support together with the abrasive or, respectively, cutting material in order to replace it when the abrasive or the cutting material has lost its effectiveness due to wear.
Experience has shown that the abrasive or cutting material loses its effectiveness rather quickly, particularly due to the fact that the stone-like material removed during working, gums the abrasive or the cutting material gradually, reducing its removal power. However, in view of the high cost of diamond, it is a primary requirement to fully utilize the abrasive or the cutting material. In this situation, at present, when gumming of the abrasive or cutting material of the tools of a machine occurs, the position of the tools in a same machine is swapped, taking advantage from the fact that gumming does not occur uniformly, so that a tool that has become gummed by working on a certain part of the stone is generally still effective if it is used on a different part of the stone, on which another tool has been working up to that time. This method allows to extend the average life of the abrasive or of the cutting material of the tool, but the result is still unsatisfactory.
The aim of the present invention is to develop a tool of the above-mentioned type, with a reduced tendency of having gummed its abrasive or cutting material, to thus maintain its operating capabilities for a considerably longer time than currently occurs.
This aim is achieved by means of the features set forth in the characterizing part of claim 1.
In particular, between the support and the connecting part a layer is interposed, made of a material which is adapted to damp the mechanical vibrations of the machine, attenuating their transmission from the connecting part to the support, and adapted to damp the vibrations that occur in the support during work, attenuating their transmission from the support to the connecting part.
The invention is based on the finding that the mechanical vibrations of the machine and the vibrations that occur in the support of the material during machining, mutually interfere, in a way which creates occasional and irregular maximums and minimums of the vibrations, which lead to uneven action of the abrasive or cutting materials on the stone. During the maximums, the stone is not worked, but rather bitten into, by the abrasive or cutting material, so that it becomes more difficult to dress or restore the abrasive or cutting material, which consequently gums up and loses its effectiveness.
The solution according to the invention prevents, or in any case considerably reduces, the possibility of mutual contact between the two separate series of vibrations. This considerably lowers the damaging effect of the mechanical vibrations of the machine, since they no longer reach the abrasive or, respectively, cutting material.
Suitably, as set forth in claim 2, the layer is constituted by a carbon-fiber fabric. Experience has shown that such a layer has, in addition to the necessary vibration-damping characteristics described above, suitable mechanical strength characteristics which are necessary in order to contrast the forces, particularly the torsional forces, that are transmitted between the support and the connecting part.
The rigidity of the layer has a decisive effect on the characteristics of the work performed on the stone and is directly linked to the aggressive or, respectively, delicate nature of the work. The higher the rigidity of the layer, the greater the strength with which the stone is bitten into during working. By adding fibers of other materials to the carbon fibers, it is possible to vary the rigidity of the layer, adapting it to the type of stone to be worked and to the type of work to be performed.
In claims 3 to 5, preferred examples of said mixed fabrics, are claimed.
In claim 6 a particularly preferred low-cost embodiment of the present invention, is claimed in which the layer is made of glass fibers dispersed in a matrix of synthetic resin. This takes into account the fact that glass fibers have mechanical characteristics which are satisfactory, although lower than those of carbon fibers, so that such fibers may be used for producing and equipping tools meant for low-value work.
If one wishes to increase the mechanical strength of the layer, conveniently, as claimed in claim 7, the layer can be obtained by vacuum formation.
As set forth in claim 8, the empty spaces of the carbon-fiber fabric are filled with silicone and the fabric is covered with a film of silicone.
Another parameter which affects the rigidity of the layer is its thickness. Suitably, as claimed in claim 9, said layer should be less than one millimeter thick, and its thickness should be, in particular, between 3 and 8 tenths of a millimeter. Layers with a thickness of approximately or exactly 3 tenths of a millimeter make possible to work the stone more aggressively than allowed by thicknesses of approximately or exactly 8 tenths of a millimeter, which are adapted for more delicate work.